Spellslinger builds, or burn decks that play a lot of instants and sorceries would make the most out of Smoldering Egg
Castle Ardenvale A classic for control decks across formats slow enough to get it going, making a token to block an attack on a planeswalker is the key function of Castle Ardenvale
Fluttershy works really well with Princess Twilight Sparkle , since most Ponies, Alicorns, Pegasi, Horses, and Unicorns have tails, allowing you to buff your entire board if you build for Twilight Sparkle's kindred ability
All Printings 5 Format Legality 13
To trigger Minn's ability, this deck often draws extra cards, including typical blue cards like Frantic Search, Opt, Thirst for Knowledge, and Behold the Multiverse